Integrated circuit with guard ring

ABSTRACT

An integrated circuit comprises an inductor over a substrate and a guard ring surrounding the inductor. The guard ring comprises a plurality of first metal lines extending in a first direction and a plurality of second metal lines extending in a second direction. The second metal lines of the plurality of second metal lines are each coupled with at least one first metal line of the plurality of first metal lines. The guard ring also comprises a staggered line comprising a connected subset of at least one first metal line of the plurality of first metal lines and at least one second metal line of the plurality of second metal lines. The first metal lines of the plurality of first metal lines outside of the connected subset, the second metal lines of the plurality of second metal lines outside of the connected subset, and the staggered line surround the inductor.

BACKGROUND

On-chip inductors are often used in integrated circuits such as radiofrequency integrated circuits (“RFIC”). Guard rings are used to isolatethe coupling of on-chip inductors to other on-chip inductors, as well asother circuit components. In one direction (1D) metal routing, guardrings are rectangular-shaped.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a diagram of an integrated circuit with a 1D metal routedguard ring, in accordance with one or more embodiments.

FIG. 2 is a diagram of a staggered line, in accordance with one or moreembodiments.

FIG. 3 is a perspective view of a staggered line, in accordance with oneor more embodiments.

FIG. 4 is a diagram of two integrated circuits in close proximity, inaccordance with one or more embodiments.

FIG. 5 is a flowchart of a method of forming an integrated circuit, inaccordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Rectangular-shaped guard rings waste space. For example, an integratedcircuit that has a rectangular-shaped guard ring for isolating anoctagonal-shaped inductor has unoccupied space between the guard ringand the inductor, which results in larger integrated circuit chips thanare necessary to perform a given function. This wasted space iscompounded and becomes further evident if more than one inductor/guardring combination is arranged on a same chip. Some integrated circuitsare designed based on one-direction (1D) or two-direction (2D) designrules. A 1D design rule describes an integrated circuit feature such asa metal line or layer that is allowed to be routed along a singledirectional path, for example, in an X or a Y direction. A 2D designrule describes an integrated circuit feature such as a metal line orlayer that is allowed to be routed along a directional path thatadvances in both the X and the Y direction to form a slanted line, forexample.

FIG. 1 is a diagram of an integrated circuit 100 with a 1D metal routedguard ring 101, in accordance with one or more embodiments.

Integrated circuit 100 comprises the guard ring 101 over a substrate103, and an inductor 105 over the substrate 103. The guard ring 101comprises first metal lines 107 a of a first metal layer 107 and secondmetal lines 109 a of a second metal layer 109. The first metal lines 107a are coupled with the second metal lines 109 a. One or more of thefirst metal lines 107 a and one or more of the second metal lines 109 aare arranged to form at least one staggered line 111 (also referred toas a zigzag or stair step line) that makes up a portion of the guardring 101. Substrate 103 comprises one or more of silicon, glass, apolymer, an oxide, or other suitable material or combination of suitablematerials.

An inductor, e.g., inductor 105, is a passive device which is used tostore energy in a magnetic field. Inductors have a measurable inductance(L), which is a measure of the magnetic field generated from aconductor. Inductance varies according to the inductor characteristicssuch as a number of loops, loop sizes, wire diameter, and other suitablecharacteristics. In some embodiments, the inductor 105 is a spiralinductor that is a circular, polygonal, or other shaped inductor that isrouted in a spiral formation. In some embodiments, the inductor 105 isoctagonal-shaped. In some embodiments, the inductor 105 iscircular-shaped. In some embodiments, the inductor 105 istriangular-shaped, hexagonal-shaped, trapezoidal-shaped, or othersuitable shape. The inductor 105 comprises a conductive material such asa metal, a metal composite, or other suitable material that is formed inone or more metallization layers by one or more of a physical vapordeposition process, a chemical vapor deposition process, a platingprocess, or other suitable process.

The inductor 105 comprises inductor contacts 105 a and 105 b. The guardring 101 surrounds the inductor 105 and makes it possible for theinductor contacts 105 a and 105 b to be coupled to one or moreconnections that are outside of the guard ring 101. For example, theguard ring 101 is configured to have one or more openings or partitionsthrough which the inductor contacts 105 a/b are coupled to a connectionoutside of the guard ring 101. The inductor contacts 105 a/b areconfigured to extend above or below the guard ring 101 to facilitatecoupling the inductor contacts 105 a and 105 b to the one or moreconnections that are outside of the guard ring 101.

In some embodiments, the first metal layer 107 is over the second metallayer 109. In other embodiments, the second metal layer 109 is over thefirst metal layer 107. The first metal layer 107 and the second metallayer 109 comprise a same or a different material or combination ofmaterials. In some embodiments, the first metal layer 107 and/or thesecond metal layer 109 comprise a conductive material such as a metal, ametal composite, or other suitable material that is formed by one ormore of a physical vapor deposition process, a chemical vapor depositionprocess, a plating process, or other suitable process.

The first metal lines 107 a extend in a first direction X. The secondmetal lines 109 a extend in a second direction Y. The first direction Xis perpendicular to the second direction Y.

Two or more of the first metal lines 107 a are offset from one anotherin one or more of the first direction X or the second direction Y. Twoor more of the second metal lines 109 a are offset from one another inone or more of the first direction X or the second direction Y. Theoffset first metal lines 107 a and the offset second metal lines 109 bare together configured to form the at least one staggered line 111. Insome embodiments, at least one of the first metal lines 107 a includedin the at least one staggered line 111 has a first length. In someembodiments, two or more first metal lines 107 a included in the atleast one staggered line 111 are of the first length. In someembodiments, at least one of the first metal lines 107 a included in theat least one staggered line 111 has a length different from the firstlength. In some embodiments, the first metal lines 107 a included in thestaggered line 111 have different lengths.

In some embodiments, the at least one of the second metal lines 109 aincluded in the at least one staggered line 111 has a second length. Insome embodiments, two of more second metal lines 109 a included in thestaggered line 111 are of the second length. In some embodiments, atleast one of the second metal lines 109 a included in the at least onestaggered line 111 has a length different from the second length. Insome embodiments, the second metal lines 109 a included in the staggeredline 111 have different lengths. In some embodiments, the first lengthis equal to the second length. In other embodiments, the first length isdifferent from the second length.

In some embodiments, one or more of the first metal lines 107 a and oneor more of the second metal lines 109 a included in the at least onestaggered line 111 overlap.

The arrangement and configuration of the first metal lines 107 a and thesecond metal lines 109 a included in the at least one staggered line 111form a guard ring 101 having the same shape as the inductor 105 whilebeing in conformance with a 1D design rule. For example, a combinationof first metal lines 107 a and second metal lines 109 a, are capable ofbeing arranged to form a guard ring 101 that is octagonal, circular,trapezoidal, elliptical, triangular, parallelogram, hexagonal,pentagonal, or other shape such as another polygonal shape, a randomshape having a staggered line that is primarily curved alone or incombination with a straight or a staggered line, or other suitableshape. In at least some embodiments, the arrangement and configurationof first metal lines 107 a and the second metal lines 109 a included inthe at least one staggered line 111 form a guard ring 101 that is adifferent shape from the inductor 105 while being in conformance with a1D design rule.

To form an octagonal guard ring 101, for example, the guard ring 101includes four staggered lines 111, two first metal lines 107 a that arecontinuous and have a length greater than the first metal lines 107 athat are included in the four staggered lines 111, and two second metallines 109 a that are continuous and have a length greater than thesecond metal lines 109 a included in the four staggered lines 111. Insome embodiments, a continuous metal line optionally comprises a seriesof metal line segments that together form a continuous metal line thathas a length greater than one of the metal lines included in thestaggered lines 111, for example.

To form a guard ring 101 that is a right triangle, for example, theguard ring 101 optionally includes one staggered line 111, one firstmetal line 107 a that has a length greater than the first metal lines107 a included in the staggered line 111, and one second metal line 109a that has a length greater than the second metal lines 109 a includedin the staggered line 111. To form a guard ring 101 that is a triangleother than a right triangle, the guard ring 101 includes two staggeredlines 111, and one of one first metal line 107 a that has a lengthgreater than the first metal lines 107 a included in the two staggeredlines 111, or one second metal line 109 a that has a length greater thanthe second metal lines 109 a included in the two staggered lines 111.

In some embodiments, the arrangement and configuration of the firstmetal lines 107 a and the second metal lines 109 a included in the atleast one staggered line 111 and/or otherwise included as a part of theguard ring 101 are arranged to be within a predetermined distance D1from the inductor 105. In some embodiments, the predetermined distanceD1 is uniform around the inductor 105.

The first metal lines 107 a first ends and second ends. The second metallines 109 a comprise first ends and second ends. In some embodiments,the first metal lines 107 a and the second metal lines 109 a overlap atthe first ends and the second ends of the first metal lines 107 a andthe second lines 109 a. In some embodiments, other portions of the firstmetal lines 107 a and the second metal lines 109 a overlap. In someembodiments, the first metal lines 107 a and the second metal lines 109a do not overlap.

FIG. 2 is a diagram of a staggered line 111, in accordance with one ormore embodiments. Staggered line 111 comprises first metal lines 107 aand second metal lines 109 a. The first metal lines 107 a extend in thefirst direction X and the second metal lines 109 a extend in the seconddirection Y. The first metal lines 107 a and the second metal lines 109a are coupled. A guard ring 101 (FIG. 1) that includes one or morestaggered lines 111 has performance properties within an allowableprocess tolerance compared to a guard ring that is formed in compliancewith a conventional 2D metal routing rule.

For example, the resistive and capacitive components of the inductor 105(FIG. 1) may adversely affect a Q-factor (Quality) and FSR(Self-Resonant Frequency) of the inductor. The Q-factor is a measure ofthe inductor efficiency and is a ratio of the inductance to resistanceat a given frequency. A higher Q-factor value indicates a lower rate ofenergy loss. The FSR of an inductor is the natural frequency in whichthe inductor oscillates freely. The integrated circuit 100, which isformed in compliance with a 1D design rule, achieves L and Q-factorvalues that are within a predefined allowable process tolerance comparedto an integrated circuit that included a guard ring formed in compliancewith a 2D design rule. A 1D design rule compliant integrated circuithaving a square or rectangular guard ring that is formed to have thesame or similar L and Q-factor values is larger than a 2D design rulecompliant integrated circuit. But, unlike conventional 1D design rulecompliant integrated circuits that have rectangular or square guardrings, the one or more staggered lines 111 form a guard ring 101 that isthe same or similar shape as the inductor 105, such as a guard ring 101that is octagonal, which reduces the space occupied by the integratedcircuit 100 compared to a conventional 1D design rule compliantintegrated circuit. For example, in some embodiments, the integratedcircuit 100 occupies a space that is 8-12% less than a space occupied bya conventional 1D design rule compliant integrated circuit that has thesame or similar L and Q-factor values.

FIG. 3 is a perspective view diagram of a staggered line 111, inaccordance with one or more embodiments. Staggered line 111 comprisesfirst metal lines 307 a and second metal lines 309 a. The first metallines 307 a extend in the first direction X and the second metal lines309 a extend in the second direction Y. The first metal lines 307 a andthe second metal lines 309 a are coupled by way of vias 301 that extendalong a third direction Z. The third direction Z is perpendicular to thefirst direction X and the second direction Y.

In some embodiments, the vias 301 comprise a conductive material such asa metal, a metal composite, or other suitable material that is formed inone or more metallization layers, through one or more layers, or betweenone or more layers such as dielectric layers, insulation layers,metallization layers, or other type of layer by one or more of aphysical vapor deposition process, a chemical vapor deposition process,a plating process, or other suitable process.

FIG. 4 is a diagram of a first integrated circuit 100 a in closeproximity to a second integrated circuit 100 b over substrate 103, inaccordance with one or more embodiments.

Because the guard rings 101 (FIG. 1) of the first integrated circuit 100a and the second integrated circuit 100 b are of the same shape as theinductor 105 (FIG. 1), a space between the inductor 105 and the guardring 101 is minimized. Additionally, the inductors 105 of the firstintegrated circuit 100 a and the second integrated circuit 100 b arecapable of being placed closer to one another. In at least someembodiments, the inductors 105 of the first integrated circuit 100 a andthe second integrated circuit 100 b are capable of being placed as closeto one another as possible. In some embodiments, a guard ring 101 of thefirst integrated circuit 100 a and a guard ring 101 of the secondintegrated circuit 100 b are arranged on the substrate 103 such that aportion of the respective guard rings 101 are separated by a distance D2that is from 0 micrometers to about 10 micrometers. Accordingly, theguard rings 101 of the first integrated circuit 100 a and the secondintegrated circuit 100 b reduce an area occupied by the first integratedcircuit 100 a and the second integrated circuit 100 b on the substrate103. In some embodiments, the first integrated circuit 100 a and thesecond integrated circuit 100 b have guard rings 101 that share asidewall, thereby making it possible to further reduce the amount ofspace occupied by the first integrated circuit 100 a and the secondintegrated circuit 100 b on the substrate 103. For example, thesidewalls of the guard rings 101 of the first integrated circuit 100 aand the second integrated circuit 100 b that are adjacent to one anotherinside of imaginary circle 401 are capable of being formed as a singlesidewall that is sharable between the first integrated circuit 100 a andthe second integrated circuit 100 b.

In some embodiments, more than two integrated circuits 100 are placednear one another over substrate 103. In some embodiments, the overallshape of the integrated circuits 100 that are placed near one anotherover substrate 103 are the same shape. In other embodiments, the overallshape of at least one of the integrated circuits 100 that are placednear one another over the substrate 103 are different shapes such that aspace occupied by the integrated circuits 100 on the substrate 103 isminimized.

FIG. 5 is a flowchart of a method 500 of forming an integrated circuit,in accordance with one or more embodiments. The method 500 isimplemented to one or more of manufacture or design an integratedcircuit such as integrated circuit 100 (FIG. 1). If method 500 isperformed to design an integrated circuit, the method 500 is implementedby a processor configured to execute a set of computer-readableinstructions that interface with a circuit design system to design andrender a layout of an integrated circuit having the features discussedherein. In step 501, an inductor such as inductor 105 (FIG. 1) is formedover a substrate such as substrate 103 (FIG. 1). In step 503, firstmetal lines such as first metal lines 107 a (FIG. 1) that extend in afirst direction are formed over the substrate. In step 505, second metallines such as second metal lines 109 a (FIG. 1) that extend in a seconddirection different from the first direction are formed over thesubstrate. In step 507, the first metal lines are coupled with thesecond metal lines. In some embodiments, the first metal lines aredirectly coupled with the second metal lines. In other embodiments, viassuch as vias 301 (FIG. 3) are formed coupling the first metal lines tothe second metal lines. The first metal lines, the second metal lines,the second metal lines, and the optional vias together form a guard ringsuch as guard ring 101 (FIG. 1) that at least substantially surroundsthe inductor.

An aspect of this description relates to an integrated circuit thatcomprises an inductor over a substrate a guard ring surrounding theinductor. The guard ring comprises a plurality of first metal linesextending in a first direction over the substrate and a plurality ofsecond metal lines extending in a second direction different from thefirst direction over the substrate. The second metal lines of theplurality of second metal lines are each coupled with at least one firstmetal line of the plurality of first metal lines. The guard ring alsocomprises a staggered line comprising a connected subset of at least onefirst metal line of the plurality of first metal lines and at least onesecond metal line of the plurality of second metal lines. The firstmetal lines of the plurality of first metal lines outside of theconnected subset, the second metal lines of the plurality of secondmetal lines outside of the connected subset, and the staggered line areconnected to form a shape surrounding the inductor.

Another aspect of this description relates to a guard ring thatcomprises guard a staggered line comprising a connected set of at leastone first conductive line segment and at least one second conductiveline segment. The at least one first conductive line segment extends ina first direction and the at least one second conductive line segmentextends in a second direction different from the first direction. Theguard ring also comprises at least one first conductive line having alength greater than one first conductive line segment. The at least onefirst conductive line extends in the first direction. The guard ringfurther comprises at least one of another staggered line, another firstconductive line, or at least one second conductive line having a lengthgreater than one second conductive line segment and extending in thesecond direction.

A further aspect of this description relates to an integrated circuitthat comprises an inductor over a substrate, first metal lines over thesubstrate, second metal lines over the substrate, and vias coupling thefirst metal lines with the second metal lines. The first metal linesextend in a first direction, and the second metal lines extend in asecond direction different from the first direction. The integratedcircuit also comprises a guard ring within a predetermined uniformdistance of the inductor substantially surrounding the inductor. Theguard ring comprises the first metal lines, the second metal lines, andthe vias. The guard ring also comprises a staggered line. The staggeredline comprises at least one of the first metal lines, at least one ofthe second metal lines, and at least one via. The staggered line couplesa first metal line excluded from the staggered line with a second metalline excluded from the staggered line.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An integrated circuit comprising: an inductorover a surface of a substrate, the inductor having a first shape; afirst metal layer over the surface of the substrate; metal lines in thefirst metal layer, wherein all metal lines in the first metal layerextend in a first direction, wherein the first direction is parallelwith the surface of the substrate, wherein the first direction is alength direction of the metal lines, and a length of each metal line inthe first metal layer is greater than a width of each metal line in thefirst metal layer; a second metal layer over the first metal layer; anda guard ring surrounding the inductor, the guard ring having a sameshape as the first shape, the guard ring comprising: a plurality offirst metal lines of the metal lines in the first metal layer; aplurality of second metal lines in the second metal layer and extendingin a second direction different from the first direction, the secondmetal lines of the plurality of second metal lines each coupled with atleast one first metal line of the plurality of first metal lines; and astaggered line comprising a connected subset of at least one first metalline of the plurality of first metal lines and at least one second metalline of the plurality of second metal lines, wherein metal lines of theplurality of first metal lines outside of the connected subset, metallines of the plurality of second metal lines outside of the connectedsubset, and the staggered line are connected to form a shape surroundingthe inductor.
 2. The integrated circuit of claim 1, wherein at least onefirst metal line of the plurality of first metal lines is offset fromanother first metal line of the plurality of first metal lines in one ormore of the first direction or the second direction.
 3. The integratedcircuit of claim 2, wherein at least one of the second metal lines ofthe plurality of second metal lines is offset from another second metalline of the plurality of second metal lines in one or more of the firstdirection or the second direction.
 4. The integrated circuit of claim 3,wherein the staggered line further comprises the at least one firstmetal line of the plurality of first metal lines and the at least onesecond metal line of the plurality of second metal lines that areoffset.
 5. The integrated circuit of claim 4, wherein the connectedsubset comprises more than one first metal line of the plurality offirst metal lines, and the first metal lines of the plurality of firstmetal lines included in the connected subset have an equivalent firstlength.
 6. The integrated circuit of claim 5, wherein the connectedsubset further comprises more than one second metal line of theplurality of second metal lines, and the second metal lines of theplurality of second metal lines included in the connected subset have anequivalent second length.
 7. The integrated circuit of claim 6, whereinthe equivalent first length is equal to the equivalent second length. 8.The integrated circuit of claim 1, wherein the guard ring is within apredetermined distance from the inductor.
 9. The integrated circuit ofclaim 8, wherein the inductor is a spiral inductor that is one ofcircular or polygonal.
 10. The integrated circuit of claim 8, whereinthe predetermined distance between the guard ring and the inductor isuniform around the inductor.
 11. A guard ring comprising: a staggeredline comprising a connected set of a plurality of first conductive linesegments and a plurality of second conductive line segments, wherein allfirst conductive line segments of the plurality of first conductive linesegments in the connected set are in a first metal layer over an uppersurface of a substrate, and all first conductive line segments of theplurality of first conductive line segments extend in a first direction,all second conductive line segments of the plurality of secondconductive line segments in the connected set are in a second metallayer over the first metal layer, and all second conductive linesegments of the plurality of second conductive line segments extend in asecond direction, different from the first direction, all firstconductive line segments of the plurality of first conductive linesegments and all second conductive line segments of the plurality ofsecond conductive line segments are parallel to an upper surface of thesubstrate, and the first and second directions are respective lengthdirections of the first conductive line segments and the secondconductive line segments, wherein the respective length directions aregreater than respective width directions of the first and secondconductive line segments; metal lines in the first metal layer, whereinall metal lines in the first metal layer extend in the first direction,and at least one metal line of the metal lines is coupled to thestaggered line; at least one first conductive line having a lengthgreater than a length of a first conductive line segment of theplurality of first conductive line segments; and at least one of anotherstaggered line, another first conductive line, or at least one secondconductive line having a length greater than one second conductive linesegment extending in the second direction.
 12. The guard ring of claim11, wherein a conductive line segment of the plurality of firstconductive line segments is offset in one or more of the first directionor the second direction from another conductive line segment of theplurality of first conductive line segments included in the staggeredline.
 13. The guard ring of claim 12, wherein at least one secondconductive line segment of the plurality of second conductive linesegments is offset in one or more of the first direction or the seconddirection from another second conductive line segment of the pluralityof second conductive line segments included in the staggered line. 14.The guard ring of claim 13, wherein every one of the plurality of firstconductive line segments included in the staggered line have anequivalent first length.
 15. The guard ring of claim 14, wherein everyone of the plurality of second conductive line segments included in thestaggered line have an equivalent second length.
 16. The guard ring ofclaim 11, wherein the at least one first conductive line and the firstconductive line segment of the plurality of first conductive linesegments are in the first metal layer, and the at least one secondconductive line and the one second conductive line segment are in thesecond metal layer different from the first metal layer.
 17. The guardring of claim 11, wherein the guard ring is polygonal.
 18. The guardring of claim 11, wherein at least one first conductive line segment ofthe plurality of first conductive line segments, the at least one firstconductive line, at least one second conductive line segment of theplurality of second conductive line segments, and the at least onesecond conductive line are electrically coupled.
 19. The guard ring ofclaim 18, further comprising: a plurality of vias that electricallycouple the at least one first conductive line segment of the pluralityof first conductive line segments, the at least one first conductiveline, the at least one second conductive line segment of the pluralityof second conductive line segments, and the at least one secondconductive line.
 20. An integrated circuit comprising: an inductor overa substrate; a first metal layer over the substrate; a second metallayer over the first metal layer; first metal lines in the first metallayer, the first metal lines extending in a first direction; secondmetal lines in the second metal layer, the second metal lines extendingin a second direction different from the first direction; vias couplingthe first metal lines with the second metal lines; and a guard ringwithin a predetermined uniform distance of the inductor, the guard ringsubstantially surrounding the inductor, the guard ring comprising thefirst metal lines, the second metal lines, and the vias, and wherein allfirst metal lines in the first metal layer that form part of the guardring extend in a same direction, wherein the guard ring comprises astaggered line, the staggered line comprises at least one of the firstmetal lines, at least one of the second metal lines, and at least onevia of the vias, and the staggered line couples a first metal lineexcluded from the staggered line with a second metal line excluded fromthe staggered line.